DESCRIPTION: (provided by the applicant) At present there is no small animal model for the study of drug abuse and neuropathogenesis in the context of HIV infection. We propose to establish such a model by adapting the existing transgenic mouse strains expressing human CD4 and CCR5 or CXCR4 developed by our collaborator Dr. D. Littman. Although hCD4/coreceptor positive T cells from these animals were found to be resistant to HIV, transgenic macrophages and microglial cells, which also express these receptors, were not tested. Our results and research by others indicate that primary rodent macrophages can efficiently replicate HIV in vitro once the block to virus entry is bypassed by pseudotyping or expression of human receptors. Since macrophages and microglia, and not T cells, are the primary targets for HIV in the brain, mouse transgenics expressing human receptors on these cells may reproduce important parameters of HIV neuropathogenesis. The overall goal of this Phase I CEBRA application is to test this possibility. Phase II studies will develop the new model further in the context of drug abuse. There are three Specific Aims: 1) To determine the viral and select cellular parameters of HIV replication in murine macrophages and microglia in vitro compared to nonpermissive murine lymphocytes; 2) To test mice transgenic for hCD4 and CCR5 or CXCR4 for receptor display in brain and lymphoid organs and to establish conditions for efficient HIV infection of murine macrophages and microglia in vivo; 3) To initiate evaluation of HIV infected transgenic mice for markers of HIV-1 neuropathogenesis. Both conventional and transgenic mouse cells will be infected in culture for assay of viral RNA and protein production, progeny virus phenotype, and selected cytokine and chemokine expression. In vivo studies shall test human CD4 and coreceptor display in microglia, macrophages, and lymphocytes and begin evaluation of HIV infection of transgenic mice by viral DNA, RNA, and protein burden in tissue and brain macrophages/microglia versus lymphocytes, and by brain tissue immunocytochemistry. These initial studies will serve as the foundation of a major program to generate mouse strains suitable for research in drug addiction in the context of productive HIV infection in the murine nervous system.